This proposal is designed to determine the structural organization of multienzyme complexes of eukaryotic aminoacyl-tRNA synthetases. The focus is the "core" complex composed of arginyl, aspartyl-, glutamyl-, glutaminyl-, isoleucyl-, leucyl-, lysyl-, methionyl- and prolyl-tRNA synthetases. Basic ultrastructural characterization will be performed, including accurate determination of molecular weight, sedimentation coefficient and shape parameters. Detailed descriptions of the complex dimensions and morphological features will be obtained using electron microscopy and fluorescence spectroscopy. Protein topography, including localization of individual synthetases within the complex and determination of their spatial arrangement, will be investigated using immunoelectron microscopy, cross-linking, fluorescence spectroscopy and limited proteolysis. The specificity and sites of interaction of the complex with other polypeptides and macromolecules will be assessed electron microscopically; specifically, the interactions with initiation and elongation factors, ribosomes, polysomes and "free" synthetases. The structural characteristics of variants of the complex will be compared with those of the normally isolated complex. This structural information is intrinsic to understanding the physiological location, functions and regulation of the aminoacyl- tRNA synthetase complex as well as its influence on other components of protein biosynthesis. These studies will further define the molecular details of the protein biosynthetic process and so aid in understanding any alterations of this process in abnormal cellular growth conditions and pathological states.